This invention relates to a cross slot antenna, and more particularly to a cross slot antenna incorporating an S-line feed.
There is a continuing need for GPS antennas (FRPA, GAS-1, CRPA, etc.) to compete for low cost, low weight GPS antennas while not compromising performance, and also a configuration that easily lends itself for providing a variety of implementations such as a single element, an antenna array, as well as a conformal antenna.
Antenna elements for circular polarization (CP) have traditionally been fabricated using expensive microwave substrate materials such as Duroids (PTFE), Alumina, and TMM. Cross slot antennas for CP have been widely used in L Band for GPS. These antennas are either cavity back antennas with various coupling techniques (wire, posts, etc.) or stripline. In addition to the high cost of using microwave materials the weight is also a significant problem for cavity backed and stripline cross slot antennas. The cost and weight are even more pronounced when integrating the antenna element in an array.
Cross slot antennas in stripline are widely used where a stripline feed network feeds the slots in quadrature. Four stripline feeds are used to couple the energy to each of the legs of the cross slot. This approach is successful for minimizing coupling between feed transmission lines and thus producing improved axial ratio. However, this approach uses expensive microwave materials in order to provide gain and radiation efficiency. The cost for raw material as well as the processing cost for an antenna array is increased significantly. In order to minimize the cost, single elements are fabricated and installed on a ground plane. This approach, although reducing fabrication cost and increasing yield, results in increased weight where in applications such as aircraft and missiles this may not be acceptable.
The physical characteristics of the S-line transmission structure and excellent electrical performance present an ideal configuration for coupling through a slot. The single slot type of antenna is a variation of the basic dipole antenna. Each side of the slot acts as one node of an elementary dipole. The length and separation dimensions of the slot are selected to maximize performance (fraction of a wavelength).
A cross slot antenna has two orthogonal intersecting crossed slots in a cavity backed conductive element where each leg of each slot is excited by an RF signal from an S-line feed providing four RF inputs of 0xc2x0, 90xc2x0,180xc2x0, and 270xc2x0 to achieve circular polarization.
The individual elements in an electronically scanned antenna are normally identical, ideally, and have two primary characteristics: (1) the beam of the element should be hemispherical, and (2) the radiation field should be circularly polarized. The criteria of a hemispherical beam enables the antenna array to have a hemispherical coverage, and circular polarization allows operation independent of the antenna orientation. The physical structure of the cross slot antenna is very well suited to array application. The major problem in the design of the cross slot antenna is the method of exciting the slots to obtain the required polarization.
In accordance with one embodiment of the present invention, a cross slot broadband antenna comprises a radiating cross slot layer having a radiating element comprising a plurality of radiating slots. A first spacer layer configured to define a cavity is positioned adjacent one side of the radiating layer wherein the cavity generally outlines the pattern of the plurality of radiating slots. An S-line transmission feed layer having feed transmission lines equal in number to the plurality of radiating slots is positioned adjacent the first spacer layer and a second spacer layer also configured to define a cavity is positioned adjacent to the transmission feed layer. In addition, the cross slot broadband antenna comprises a ground plane layer having a copper clad surface, where the ground plane layer is positioned adjacent the second spacer layer.
Also in accordance with the present invention there is provided a cross slot broadband antenna comprising a radiating cross slot layer having a plurality of radiating elements, each radiating element comprising a plurality of radiating slots to form an array of radiating elements. A first spacer layer configured to define a cavity in proximity to each of the plurality of radiating elements is positioned adjacent one side of the radiating layer. Positioned adjacent the first spacer layer is an S-line transmission feed layer having three transmission lines equal in number to the plurality of radiating slots for each of the plurality of radiating elements. A second spacer layer also configured to define a cavity for each of the plurality of radiating elements is positioned adjacent to the transmission feed layer. Positioned adjacent the second spacer layer is a ground plane layer having a copper clad surface.
Technical advantages of the present invention include providing an S-line cross slot antenna constructed utilizing common, low cost, light and each to process materials relative to the microwave substrates typically utilized. Further, size reduction is a technical advantage along with configuring the antenna to provide flush mounting of the antenna. As a result, the S-line cross slot antenna has superior physical characteristics and electrical performance and presents a new idea of configuration for coupling energy to the slot type antenna.